SIR Installation
To install SIR on Ubuntu 11.10/11.04, run these commands from the Terminal:
sudo add-apt-repository ppa:rsachetto/ppa
sudo apt-get update
sudo apt-get install sir
Launch SIR using the Unity Dash and click Add File or Add Dir to start resizing your images to any dimensions of your choice.
Source: http://www.upubuntu.com/2011/11/sir-simple-tool-to-batch-convert-and.html